A redox type fuel cell is a fuel cell in which at least one of a fuel and an oxidant is reacted with a redox couple (mediator), instead of being directly reacted in electrodes, and the redox couple is reacted in at least one of an anode electrode and a cathode electrode. The redox type fuel cell is characterized in that it has long lifetime or it does not need to use an expensive catalyst (e.g., platinum) in electrodes.
In a fuel cell in which a hydrogen gas is used as a fuel and an oxygen gas is used as an oxidant, generally, an oxygen reduction reaction is slow and constitutes a large part of fuel cell polarization. Accordingly, there is a well-known redox type fuel cell in which a hydrogen gas is supplied to an anode electrode and a redox couple-containing solution is supplied to a cathode electrode only.
A redox type fuel cell is described in Patent Literature 1, in which a mediator-containing nonvolatile catholyte solution is circulated between a cathode and a regenerator, and the mediator reduced in the cathode during discharge is reacted in the regenerator by oxygen injection, thereby oxidizing and regenerating the mediator.